Move setup-uv to v9 (#65)

Found in a workspace-wide Actions audit: this was the last Python repo
still on `astral-sh/setup-uv@v8.3.2` (3 sites: ci, security, publish).
python-commerce already took v9.0.0 via Dependabot and runs it green.

v9's only breaking change is the `prune-cache` default flipping to
`false`, which changes Actions cache size rather than behaviour, and the
uv cache here is managed by its own `actions/cache` step rather than
setup-uv's.

Everything else in this repo audited current.

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: vvillait88

.github/workflows/ci.yml

@@ -20,7 +20,7 @@ jobs:
     timeout-minutes: 10
     steps:
       - uses: useblacksmith/checkout@v1
-      - uses: astral-sh/setup-uv@v8.3.2
+      - uses: astral-sh/setup-uv@v9.0.0
       - run: uv python install 3.12
       - uses: actions/cache@v6
         with:

.github/workflows/publish.yml

@@ -19,7 +19,7 @@ jobs:
     steps:
       - uses: actions/checkout@v7
 
-      - uses: astral-sh/setup-uv@v8.3.2
+      - uses: astral-sh/setup-uv@v9.0.0
 
       - name: Set version from tag
         run: sed -i "s/^version = .*/version = \"${GITHUB_REF_NAME#v}\"/" pyproject.toml

.github/workflows/security.yml

@@ -36,7 +36,7 @@ jobs:
     timeout-minutes: 5
     steps:
       - uses: useblacksmith/checkout@v1
-      - uses: astral-sh/setup-uv@v8.3.2
+      - uses: astral-sh/setup-uv@v9.0.0
       - uses: actions/setup-python@v7
         with:
           python-version: "3.13"